The present invention relates to a steering resistance system for a drive-by-wire vehicle steering system and, more particularly, to a steering resistance system using a viscous damper to impart rotary resistance to the steering wheel in a drive-by-wire vehicle steering system for agricultural and construction vehicles.
Vehicle steer-by-wire systems in construction and agricultural applications are advantageous in that they replace bulky, complicated mechanical steering systems typically located and required to operate in harsh environmental conditions with components that may be located in less severe environments. Typical steer-by-wire systems take operator input in the form of steering wheel rotation and communicate that input to the steered wheels through non-mechanical means. However, eliminating the mechanical linkage between the steering wheel and the steered wheels removes traditional sources to steering wheel movement resistance, such as friction within the steering linkage, and the forces required to reposition the steered wheels. The steering wheel is thus free to rotate with negligible resistance. Without adequate resistance to steering wheel rotation, inadvertent steering inputs may be sensed by the steer-by-wire system caused by vehicle vibration, inadvertent operator movement, or both. Steering wheel resistance is also needed to prevent the operator from providing more steering input than desired in response to normal field conditions when little or no resistance to the input is encountered thereby resulting in a vehicle oversteering condition.
Numerous inventions address the problem of steering wheel feedback through use of complex systems that simulate the steering wheel feel and/or motion traditionally experienced with a conventional mechanical steering linkage. Many of these inventions employ complex systems for sensing reactions at the steered wheels and translating the reactions into steering wheel motions via elaborate motor and resistance units. Such systems are generally intended for automobiles where vehicle speeds dictate that more sensory feedback be provided from the steered wheels. Complex steering wheel feedback systems are expensive, resulting in unnecessary expense in agricultural vehicles. Additionally, complex systems may lack the necessary reliability for agricultural and construction applications; equipment down time, especially during critical harvest times, jeopardizes the crop and represents additional economic disadvantages to the complex systems.
Elaborate steering wheel feedback systems in agricultural and construction are unnecessary and are, in fact, undesirable. Vehicle speeds are comparatively low and the benefit of providing sensory feedback from the steering wheel to the vehicle operator negligible. Adequate steering wheel feel in a steer-by-wire system can be accomplished by adding torsional resistance to the steering wheel to prevent it from freely spinning when turned, such as a friction brake. Friction brakes are disadvantageous because of inherent differences between static and dynamic friction coefficients which result in differing levels of steering wheel resistance during a turning cycle. The vehicle operator initially experiences a high resistance to steering wheel movement followed by lower resistance once steering wheel movement commences. Operator effort to cause initial steering wheel movement can result in greater directional input than is needed or intended once the steering wheel begins to rotate. Correcting such steering inputs increases operator fatigue during vehicle operation which can adversely affect vehicle productivity during critical harvest seasons.
It would be a great advantage to provide a simple damping system to a steer-by-wire steering wheel that provides passive resistance to steering wheel rotation based on the speed of the rotation, avoids complex steering wheel feedback systems, and overcomes the above problems and disadvantages.